A number of microorganisms having beneficial effects on plant growth and health are known to be present in the soil, to live in association with plants specifically in the root zone (rhizosphere-associated bacteria), or to reside as endophytes within the plant. Their beneficial plant growth promoting properties include nitrogen fixation, iron chelation, phosphate solubilization, inhibition of non-beneficial microorganisms, resistance to, or exclusion of pests, Induced Systemic Resistance (ISR), Systemic Acquired Resistance (SAR), decomposition of plant material in soil to increase useful soil organic matter, and synthesis of phytohormones such as indole-acetic acid (IAA), acetoin and 2,3-butanediol that stimulate plant growth, development and responses to environmental stresses such as drought. In addition, these microorganisms can interfere with a plant's ethylene stress response by breaking down the precursor molecule, 1-aminocyclopropane-1-carboxylate (ACC), thereby stimulating plant growth and slowing fruit ripening. These beneficial microorganisms can improve soil quality, plant growth, yield, and quality of crops. Various microorganisms exhibit biological activity such as to be useful to control plant diseases. Such biopesticides (living organisms and the compounds naturally produced by these organisms) are generally considered safer and more biodegradable than synthetic fertilizers and pesticides.
For example, beneficial plant associated bacteria, both rhizospheric and endophytic, are known to provide a multitude of benefits to host plants that ranges from resistance to diseases and insects pests and tolerance to environmental stresses including cold, salinity and drought stress. As the plants with inoculated plant growth promoting bacteria acquire more water and nutrients from soils, e.g. due to a better developed root system, the plants grow healthier and are less susceptible to biotic and abiotic stresses. As such the microbial compositions of the present invention can be applied alone or in combination with current crop management inputs such as chemical fertilizers, herbicides, and pesticides to maximize crop productivity. Plant growth promoting effects translate into faster growing plants and increase above ground biomass, a property that can be applied to improve early vigor. One benefit of improved early vigor is that plants are more competitive and out-compete weeds, which directly reduces the cost for weed management by minimizing labor and herbicide application. Plant growth promoting effects also translate into improved root development, including deeper and wider roots with more fine roots that are involved in the uptake of water and nutrients. This property allows for better use of agricultural resources, and a reduction in water used in irrigation needs and/or fertilizer application. Changes in root development and root architecture affect the interactions of the plant with other soil-borne microorganisms, including beneficial fungi and bacteria that help the plant with nutrient uptake including nitrogen fixation and phosphate solubilization. These beneficial microbes also compete against plant pathogens to increase overall plant health and decrease the need for chemical fungicides and pesticides. A more developed root system also allows for improved yields when pests are present.
Fungal phytopathogens, including but not limited to Botrytis spp. (e.g. Botrytis cinerea), Fusarium spp. (e.g. F. oxysporum and F. graminearum), Rhizoctonia spp. (e.g. R. solani), Magnaporthe spp., Mycosphaerella spp., Puccinia spp. (e.g. P. recondita), Phytopthora spp. and Phakopsora spp. (e.g. P. pachyrhizi), are one type of plant pest that can cause severe economic losses in the agricultural and horticultural industries. Chemical agents can be used to control fungal phytopathogens, but the use of chemical agents suffers from disadvantages including high cost, emergence of resistant strains of pests, and potentially undesirable environmental impacts. In addition, such chemical treatments may adversely affect beneficial bacteria, fungi, and arthropods in addition to the plant pest at which the treatments are targeted. A second type of plant pest are bacterial pathogens, including but not limited to Erwinia spp. (such as Erwinia chrysanthemi), Pantoea spp. (such as P. citrea), Xanthomonas (e.g. Xanthomonas campestris), Pseudomonas spp. (such as P. syringae) and Ralstonia spp. (such as R. soleacearum) that cause severe economic losses in the agricultural and horticultural industries. Similar to pathogenic fungi, the use of chemical agents to treat these bacterial pathogens suffers from disadvantages. Viruses and virus-like organisms comprise a third type of plant disease-causing agent that is hard to control, but to which bacterial microorganisms can provide resistance in plants via induced systemic resistance (ISR). Thus, microorganisms that can be applied as biofertilizer and/or biopesticide to control pathogenic fungi, viruses, and bacteria are desirable and in high demand to improve agricultural sustainability. A final type of plant pathogen includes plant pathogenic nematodes and insects, which can cause severe damage and loss of plants and reductions in yield.
Some members of the species Bacillus have been reported as biocontrol strains, and some have been applied in commercial products (Joseph W. Kloepper, et al. 2004, Phytopathology Vol. 94, No. 11, 1259-1266). For example, strains currently being used in commercial biocontrol products include: Bacillus pumilus strain QST2808, used as active ingredient in SONATA and BALLAD-PLUS, produced by BAYER CROP SCIENCE; Bacillus pumilus strain GB34, used as active ingredient in YIELDSHIELD, produced by BAYER CROP SCIENCE; Bacillus subtilis strain QST713, used as the active ingredient of SERENADE, produced by BAYER CROP SCIENCE; Bacillus subtilis strain GBO3, used as the active ingredient in KODIAK and SYSTEM3, produced by HELENA CHEMICAL COMPANY. Various strains of Bacillus thuringiensis and Bacillus firmus have been applied as biocontrol agents against nematodes and insects and these strains serve as the basis of numerous commercially available biocontrol products, including DIPEL comprising a Bacillus thuringiensis subsp. kurstaki strain, produced by VALENT BIOSCIENCES CORPORATION, and NORTICA and PONCHO-VOTIVO comprising a B. firmus strain, produced by BAYER CROP SCIENCE. In addition, Bacillus strains currently being used in commercial biostimulant products include: Bacillus subtilis var. amyloliquefaciens strain FZB42 used as the active ingredient in RHIZOVITAL 42, produced by ABiTEP GmbH, as well as various other Bacillus subtilis species that are included as whole cells including their fermentation extract in biostimulant products, such as FULZYME produced by JHBiotech Inc.
However, it is desirable to develop new compositions and methods for benefiting plant growth and controlling plant pests.